Alloy steel



loying constituents.

Patented June 19,1945

UNITED STATES PATENT OFFICE ALLOY STEEL Byramji D. Saklatwalla,Pittsburgh, Pa.

No Drawing. Application January 19, 1943, Serial No. 472,855

Claims.

This invention relates to'an alloy steel intended for structuralpurposes and possessing in the asrolled state high strength andcorrosion resistance. My steel is low in carbon and silicon contents,with a comparatively lowmanganese content, and containing chromium,nickel, copper, molybdenum and phosphorus as the effective al- Thechromium, nickel, and molybdenum are employed as strength-impart:

ing agents in the steel and when employed in properly balancedproportions to each other and to the other strength-imparting elements,phosphorus and copper, are found to impart strength without impairingthe ductility of the steel, as would be the case were the strengthobtained from appreciable contents of carbon,- silicon and/ ormanganese, which are the usual strengthimparting elements in carbon oralloy steels. Contents of chromium, copper, phosphorus, nickel, andmolybdenum are incorporated in the steel, in certain selected ranges;such as to impart to the steel a, high degree of corrosion resistance.

, All the elements are used in such balanced proportions thatsimultaneously strength and corrosion resistance of a high degree areobtained in the steel, permitting reduction of sections and totalweight, without sacrifice of life of structures constructed of thesteel. y

In the older high-strength corrosion-resistant copper-phosphorus steelscontaining chromium or those containing chromium and molybdenum ornickel and molybdenum, their high strength properties are obtainedessentially by the presence of an appreciable silicon content, specifiedto be from .25 or .35% up to 2 and even up to 3%. Such high siliconsteels require particular care during their melting and refining in theopen-hearth furnace, and in the process of casting soaking and heatingof their ingots prior to the rolling operation. Such extra care isessential in order to obtain the finished rolled steel with a cleanstructure and in a seam-free and good surface condition. Moreover, highsilicon steels are usually produced by casting the ingots with hot-topsentailing extra time and cost in their production. If, to obviate thesedeficiencies, the silicon content of th steel is lowered, the requiredstrength properties are not obtained, the silicon being the essentialstrength-imparting element in such steels. 1

I obviate the above deficiencies and produce by my invention acorrosion-resistant copper-phosphorus steel, although lowin silicon,manganese, and carbon, yet with high tensile strength and yield pointand capable of being produced by the open-hearth process practicallywith equal facility as ordinary low-carbon steel. I accomplish this byincorporating in the copper-phosphorus steel a combination of chromium,nickel, and

5 molybdenum within certain definite ranges.

When chromium alone with copper and phosphorus is used, as in the oldersteels, the requisite tensile strength and yield point are not obtainedunless the high percentage of silicon -(.25 to 30%) is present.Similarly, when chromium and molybdenum alone, or nickel and molybdenumalone, are used with copper and phosphorus, the high percentage ofsilicon (.35 to 2.0%) has to be present in the steel to obtain thespecified strength properties. If nickel alone is used with copper andphosphorus, the amount of nickel necessary to obtain the strength is sohigh as to make the steel unduly expensive. If with a smaller amount ofnickel, a large percentage of copper, such as would be necessary toobtain the strength,.is used, the steel becomes subject to precipitationhardening when cooled from a high temperature and possesses a low degreeof formability and workability. If a high manganese contents, over .5and up to 1.25% manganese, is usedto impart strength to copperphosphorussteels, such manganese content curtails ductility and especially theimpact resistance of the steel, at the same time making it difflcultlyweldable, owing to the hardening action of the manganese when coolingfrom welding temperature.

By my composition, in which the percentages 'of the various alloyingelements are used in bal "anced proportion against one another, Iobtaina corrosion-resistant steel which has all the wellknown manufacturingadvantages of a low-silicon open-hearth steel, such as easy melting andrefining and ingot-casting practice. Moreover, with this case inmanufacturing, the steel possesses a higher degree of ductility, impactresistance, and weldability than the high silicon and/or high manganesesteels, at the same time displaying strength properties equal to thoseof such steels. Furthermore, the elements chromium, nickel, copper,molybdenum and phosphorus are used in my steel in such combinations andproportions as to impart .to the steel a corrosion resistance severaltimes greater than that of ordinary carbon or copper-bearing steel,enabling it to withstand corrosive conditions to which structural steelsare ordinarily subjected in use. I have found that when the elements areused in 66 t e specified ranges, the best balance of strength,

Per cent Carbon .01 to less than .14 Silicon .01 to less than .18Manganese .05 to less than .50 Phosphorus .07 to .18 Chromium .25 to 1.5Nickel .25 to 1.25 Molybdenum .07 to .60 Copper .18 to .75

The following is a more restricted range of elements for the productionof the steel:

in two inches based on a 2-inch gage length specimen. Practically allthe steels falling with- Per cent Carbon .05 to .13 Silicon .01 to .12Manganese .15 to .45 Phosphorus .08 to .15 Chromium .35 to 1.0 Nickel.30 to .90 Molybdenum .08 to .35 Copper .25 to .65

A still more restricted range within which steels of well balancedproperties can be produced is as follows:

a Per cent Carbon .06 to .12 Silicon .03 to .10 Manganese .20 to .40Phosphorus .08 to .13 Chromium .40 to .85 Nickel .40 to .75 Molybdenum.10 to .30 Copper .30 to .60

I prefer to keep the manganese content low, as I have found that anysubstantiallyhigh manganese content of the steel is deleterious,inasmuch as it lowers the impact resistance and weldability of thesteel. The manganese content of the steel must be maintained below amaximum of .5%.

The sulphur content should be low, as in good steel-making practice, inwhich it is under .05%. I prefer that the sulphur content. be as low aspossible, preferably under .03%.

The balance of my composition is made up of commercial steel with theusual impurities derived from the raw materials used in the making ofthe steel, such as ore, fuel, fluxes, scrap, etc. If desired, the steelcan be treated with the usual deoxidizing and refining agents, such asaluminum, term-titanium, term-zirconium, ferrovanadium, ferro-boron,etc., or with the complex deoxidizers, such as silicon-calcium,silicon-aluminum-calcium, silicon-zirconium-calcium, or with theso-called intensifier agents containing a plurality of refiningelements.

The steel of my composition, owing to its low carbon and siliconcontents, possesses a high dein the above ranges of composition arecapable of meeting the usual commercial specifications for high tensilesteels; namely, over 70,000 lbs. per square inch tensile strength and.over 50,000 lbs. per square inch yield point. The steels possess an Izodvalue generally of about 40 footpounds or over. They possess goodwelding, bending and forming properties. It is an essentialcharacteristic of the steel that it possess low hardenability, so thatin the process of welding, hardening adjacent to the weld does not takeplace. These properties are obtained in the steel in the as-rolledcondition without any expenditure for heat treatment which is animportant economic advantage.

The elements nickel, molybdenum, and copper used in my steel beingnotoxidizable are fully recovered from the scrap. Owing to the recovery ofthese ,expensiveelements from the scrap, and as no heat treatment isrequired. to obtain the desirable balanced properties of the steel, itbeing used in the asrolled condition, the fabrication of weldedstructures such as railroad cars, ships and other transportation unitscan be accomplished with this steel at a relatively cheap cost.

The steel of my invention can be produced by the'ordinary steel-makingprocesses, such as the open-hearth, electric furnace, or converterprocess. The nickel, copper, and molybdenum can be added in the furnace,during the melting and refining of the steel, according to the usualpractice. The chromium, as ferro-chrome, and the phosphorus, asferro-phosphorus, can be added in the furnace, but it is preferable toadd them in the ladle after tapping the steel to avoid unnecessary lossof these elements throughoxidation and to more easily control theircontent in the finished steel.

I claim:

1. A corrosion resistant, low-carbon, low-alloy high strength steel withsilicon and -manganese contents not in excess of those found in mildcarbonsteel, and being under the contents required for imparting addedstrength to carbon steels, the silicon being less than about .18% andthe manganese less than about .50%, together with a carbon content offrom .01% to less than 14%, and containing as essential alloyingconstituents chromium from .25% to 1.5%, nickel from .25%

to 1.25%, molybdenum from .07% to .60%, copper from .18% to .75%, andphosphorus from .07% to .1'8%, the balance being commercial steel, andcharacterized in the as-rolled conditionfl;

' both high tensile and high yield strengths, to-

gether with a greater degree of ductility and impact resistance than isfound in copper-phosphorus steel of equivalent tensile strength andcontaining silicon in excess of .18% or manganese in excess of 50%.

2. A corrosion resistant, low-carbon, low-alloy high strength steel withsilicon and manganese contents not in excess of those found in mildcarbon steels, and being under the contents required for impaiting addedstrength to carbon steels, the silicon being less than about .12% andthe manganese less than about .45%, together with a carbon content offrom .05% to less than .13 and containing as essentialalloying-constituents chromium from 35% to 1.0%, nickel irom 30% to.90%, molybdenum from to .35%, copper from .25% to .65%, and phosphorusfrom .08 to .15%, the balance being commercial steel, and characterizedin the as- 2,878,487 rolled condition by both high tensile and highyield strengths, together with a greater degree of ductility and impactresistance than is found in copper-phosphorus steel of equivalenttensile strength and containing silicon in excess of .18%

or manganese in excess of .50%.

3. A corrosion resistant, low-carbon, low alloy high strength steel withsilicon and manganese contents not in excess of those found in mildcarbon steels, and being under the contents required for imparting addedstrength to carbon steels, the silicon being less than about .10% andthe manganese less than about .40%, together with a carbon content offrom .06% to .12%, and containing as essential alloying constituentschromium from .40% to 35%, nickel from .40% to 375%, molybdenum from.10% to 30%, copper from .30% to .60%, and phosphorus from .08% to 13%,the balance being commercial steel, and characterizedin the as-rolledcondition by both high tensile and high yield strengths, together with agreater degree of ductility and impact resistance than is found incopper-phosphorus steel of equivalent tensile strength and containingsilicon in excess of .18% or manganese in excess of .50%.

iii

4. A corrosion resistant, low-carbon, low-alloy high strength steel withsilicon and manganese contents not in excess found in mild carbonsteels, the silicon being less thanabout .18% and the manganese lessthan about 50%, together with a carbon content of less than about 14%,and containing as essential alloying constituents chromium from 25% to1.5%, nickel from 25% to 1.25%, molybdenum from .07% to .60%, copperfrom .18% to 315%, and phosphorus from .0'-7% to .18%, the andcharacterized in the as-rolled condition by a relatively high ratio ofductility to tensile strength.

5. A corrosionresistant, low-carbon, low-alloy high strength steelcontaining as essential alloying constituents chromium from 25% to 1.5%,nickel from 25% to 1.25%, molybdenum from 07% to .60%, copper from .18%to .75%, and phosphorus from 07% to .18%, together with carbon from .01to less than 4%, silicon from .01 to less than .18%, and manganese from.05 to less than 50%, the balance being commercial steel.

BYRAMJI D. SAKLATWALLA.

balance being commercial steel, 4

